During storage and handling operation of glass articles such as glass plates, glass bottle, glass tubes, glass bulbs and other glass products, glass surfaces are often contaminated by dust, dirt, moisture or others, cracked and/or streaked by touch or collision with any other objects, or weathered in long time. As a result, the glass articles have defects before use and cannot actually be used. For example, it is impossible to supply cracked or streaked glass plates in commerce for window glass plates. Contaminated glass bottles cannot be used for containers of drinks, foods and pharmaceuticals. Glass parts having those defects cannot be used at all in electric and electronic products such as cathode ray tubes (CRTs), liquid crystal displays (LCDs) or others.
Therefore, it is well known in the prior art to coat a glass surface of a glass article with a surface-protection coating. The coating is a layer or film of any substance for protecting the glass surface from streak and/or crack, weathering, and contamination by dirt, moisture and others during storage and handling operation. It is desired that the surface-protection coating can readily removed in practical use of the glass article.
Japanese patent publication No. 45-1193 (that is, No. 1193/1970, which will be referred to as Reference I) discloses a glass plate having a surface-protection coating which is soluble in water and, therefore, readily removed by water washing. The surface-protection coating is of ethylene-maleic acid copolymer with a bridged structure and is formed by applying a water solution of the copolymer onto a glass surface of the glass plate.
JP-A-46 48061 (Reference II) discloses to form a water-soluble thin coating of a nonionic surfactant on a glass surface of a glass bottle by spraying a water solution of polyoxyethylene alkyl phenol ether to the glass bottle.
JP-A-56 25970 (Reference III) discloses to form a water-soluble thin coating of silicate on a glass surface of a glass substrate by spraying a water solution of silicate to the glass substrate.
JP-A-4 11981 (Reference IV) discloses to form a thin coating of water-soluble plastic resin on a glass surface of a glass substrate by applying a water solution of plastic resin to the glass substrate. The water-soluble plastic resin is at least one selected from polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, methyl cellulose, polyethylene oxide, polyvinylpyrrolidone, pyrrolidone vinyl acetate copolymer, methyl vinyl maleic acid copolymer, and acrylic acid-methacrylic acid ester copolyer.
JP-A-6 340865 (Reference V) discloses a glass substrate coated with a water-soluble salt such as sodium tripolyphosphate, sodium sesquicabonate, sodium hydrogencarbonate, sodium carbonate, sodium tetracarbonate, or potassium tetracarbonate.
JP-A-7 10600 (Reference VI) discloses a glass article such as glass bottle with a water-soluble coating such as phosphate, borate, silicate, sulfate, inorganic salt including sulfur, halide, carbonate, bicarbonate, nitrate, organic acid salt, double salt of those slats, organic acid, monosaccharides, and polysaccharides. Some of sodium salts are disclosed as the salts actually used.
As described above, it is known in the prior art that organic substances are used for water-soluble surface-protection coating of glass article. However, it is desired that organic substances are avoided from use for such coatings, because the organic substances may often cause the environmental pollution after being washed away by water.
The use of inorganic salts is also known in the prior art as disclosed in References III, V and VI. Among various inorganic salts, sodium salt is known superior in water solubility, and, therefore, useful for the water-soluble surface-protection coating. However, sodium ions in the coating unfortunately degrade the glass surface on which the coating is applied. The use of salts of other alkali metals has the similar problem.
On the other hand, JP-A-3 44857 (Reference VII) discloses a protective film or sheet attached by use of adhesive agent onto an outer face of a CRT tube for protecting a screen face. However, the adhesive agent used often contaminates the face and/or other area of the CRT. Further, there is a problem for wasting the protective sheet after being removed from the CRT.
It is also well known in the prior art to bring a glass article into contact with sulfuric acid gas or hydrochloric acid gas to form a protective layer. This is disclosed in, for example, JP-A-2 120256 (Reference VIII). The protective layer is a chemical compound of sodium in the glass with the gas. The protective layer can be washed out by water. However, since sulfuric acid gas or hydrochloric acid gas is used, there are problems in apparatus and safety.